1. Field of the Invention
The present invention relates to a method for manufacturing a stainless steel product and a stainless steel product manufactured by the method.
2. Related Prior Arts
Conventionally, in order to produce a stainless steel product with good workability and corrosion resistance, Japanese Un-Examined Patent Application Publication No. 2004-68115, for example, proposes a method of manufacturing a stainless steel product by nitrogen absorption treatment, comprising the steps of bringing a bulk product of a ferritic stainless steel having been formed into a desired shape through melting and machining, into contact with an inert gas containing nitrogen gas at 800 degrees C. or above, and austenitizing the product either wholly or partially to form a two-phase structure comprised of ferrite and austenite.
Further, Japanese Un-Examined Patent Application Publication No. 7-188733, for example, proposes a thermal treatment process for improving friction resistance due to the structural components of ferrite and martensite being made austenitic in the surface region of stainless ferritic-austenitic duplex steel X 2CrNiMoN2253 through the nitrogen enrichment at 1,000 to 1,200 degrees C.
Furthermore, Japanese Un-Examined Patent Application Publication No. 5-311336, for example, proposes a chromium-based stainless steel plate comprised of 13.0 to 20.0% by weight of Cr, 0.1 or lower % by weight of C and 0.1 or lower % by weight of N, and Fe and unavoidable impurities as the remainder, said stainless steel plate including a nitrogen enriched layer.
As is apparent from the foregoing, the foregoing prior art documents propose austenitizing through nitrogen absorption treatment. Specifically, according to the technique disclosed by Japanese Un-Examined Patent Application Publication No. 2004-68115, it is possible to produce a stainless steel product with good workability and corrosion resistance. According to these prior arts, however, there still remain some problems to be solved for actual mass production, such as improvement of nitrogen absorption efficiency and control of grain coarsening in the nitrogen absorption process.
In recent years, Ni-free ferritic stainless steel has been used as a material for a side member of a watch or the like that is to be directly contacted by a human body, as is proposed in Japanese Un-Examined Patent Application Publication No. 2000-8145. Ferritic stainless steel, however, is inferior to austenitic stainless steel in respect of corrosion resistance and strength.